Using Latex online

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http://www.sciweavers.org/free-online-latex-equation-editor

You can cut and paste things like

\flushleft

  x(u) = \begin{bmatrix}1 \\ 1 \\ 0 \end{bmatrix} \\

  y(i) = \begin{bmatrix}0 \\ 1 \\ 0 \end{bmatrix} \\

\centering\\

\flushleft

preference: p(u,i) = x^\intercal(u) * y(i)\\

\centering\\

\flushleft

min  \sum\limits_{u,i} (r(u,i) - p(u,i))^2 +  \lambda (||x(u)||^2 + ||y(i)||^2)